Corrosion inhibition



United States Patent() CORROSION INHIBITION Arnold J. Rosenthal,Whippany, NJ assignor to Celanese Corporation of America, New York,N.Y.,a corporation of Delaware No Drawing. Application May 31, 1957Serial No. 662,602

20 Claims. (Cl. 106-14) The present invention relates to the preventionof corrosion of metals by solutions of organic acid esters of cellulosein halogen-containing organic solvents. More particularly, it relates tonovel processes for preventing such corrosion by incorporation in thesolution of special stabilizing agents.

In the course of converting organic acid esters of cellulose tofilamentary material and the like, these esters may be dissolved inhalogen-containing organic solvents. By way of illustration, cellulosetriacetate is dissolved in methylene chloride which may also containminor amounts of co-solvents for the ester such as methanol, ethanol,isopropanol or the like, as well as small amounts of water. Thissolution or dope is then dry spun into filamentary cellulose triacetate,the solvent being evaporated by a current of warm air followed byrecovery and purification prior to re-use. The spinning is effected bypassage of the solution through one or more orifices in a metallicmember in the art referred to as a jet. It has been found that thesejets as well as other metal equipment contacted by the solvent duringuse and recovery c rrode rapidly and require frequent replacement.

It is accordingly an object of the present invention to minimize orprevent this corrosion of metallic members contacted byhalogen-containing organic solvents for organic acid esters ofcellulose.

It is a further object to incorporate in solutions of organic acidesters of cellulose in halogen-containing or-, 'ganic solvents astabilizer which will inhibit or eliminate corrosion of iron or steelcontacted therewith.

Another object is to provide a solution of cellulose triacetate inmethylene chloride, which solution can be dry spun without rapidcorrosion of the spinning jet.

Other objects of this invention will be apparent from the followingdetailed description and claims.

In accordance with the present invention, to a halogencontaining organicsolvent solution of the organic acid ester of cellulose there is added astabilizer which inhibits corrosion of metallic members. The stabilizersmust satisfy certain requirements in order to be suitable for. use,viz., they must themselves be non-corrosive, they.

should not have any particular affinity for the cellulose ester lestthey contaminate articles produced therefrom,

understood. While it might be expected that the corrosion is the resultof the presence of hydrohalic acids,1stabilizers heretofore used toprevent corrosion in other systems or contaniing organic solvents. Theeifective stabilizers in-v 'alone or in admixture. I V p lower alkylamines and especially hydroxysubstituted .sary'.

' The solvent. of the cellulose ester solution can be any Patented Mar.1, 1960 systems, e.g., organometal salts or acid binding agents such astriethylamine and triethanolamine, are ineffective 'in'the instantsituation. Moreover, the corrosion of the spinning jets is apparentlyindependent of temperature,

"oxidation but 'faces of jets exposed to air are even less corroded thanthose shielded from air. In addition, antioxidants such as hydroquinoneethers donot exert any appreciable inhibitory effect on solutions of thecharacter herein set forth. j. 3

It has now been found thata limited group of organic compounds iseffective in avoiding the corrosion of metals by solutionsof organicacid'esters of cellulose in halogencludeamine nitrites and cadmiumsaltsofiatty acids, Of the amine nit-rites, nitritesof lower alkylamines such as 2-hydroxyproplyamine are preferred; of the cadmium saltsof fatty acids, those of waterinsoluble fatty acids and especiallywater-insoluble alskanoic acids such as 2-ethyl hexoic acid arepreferred.

The stabilizers will exert some beneficial action even in the smallestamountsbut for appreciable inhibition they should be present in at leastabout 0.005% by weight ofthe solution. Generally, at least about 0.01%by weight is employed and preferably about 0.05%. As much as 0.5% oreven more can be used but since corrosion is substantially completelyeliminated with lesser :amounts there is no point in adding morestabilizer than is neceshalogenated organic solvent but the preferredsolvents are chloLne-substituted lower alkanes such as methylenechloride, ethylene dichloride, and the like. contain minor amounts ofco-solvents or non-solvents for the esters, depending upon theproperties desired for the composition and the subsequent treatments towhich it will be subjected. When a methylene chloride solution is to beused for'dry-spinning, for example, the methylene chloride solvent maycontain as much as 20% 'by weight stabilizing action will be realizedeven in the presence of water.

Organic acid esters of cellulose which can be' used arepreferably thelower alkanoic acid esters such as the acetate, propionate, butyrate,acetate-propionate, acetatebuty rate, and the like. While the inventionis applicable to any esters which will dissolve in the indicatedsolvents,

' excellent' results are achieved whenusingcellulose acetate having anacetyl content in excess of about 59.5% and preferably 61.5% by weightcalculated as acetic acid.

to bind any decomposition products of halogen-containing Such esters aresubstantially fully acetylated, i.e., free of unreacted hydroxy groups,and are hereinafter referred to as cellulose triacetate although a smallresidue of unreacted hydroxy-groups may be present. The presentinvention is particularly useful in the dry spinning of solutions ofcellulose triacetate in methylene chloride-methanol, such as aredisclosed in copending US. application Serial No. 566,088,..filedFebruary 17, 1956, by Robert K. Davies and'Arnold J. Rosenthal.

The solutions there described comprisecellulose acetates having anacetyl value in excess of 59.5% by weight expressed as acetic acid(herein referred to as cellulose triacetate) dissolved in methylenechloride-methanol to These may a concentration of above 15% andpreferably from 17 to 27%. The methylene chloride can range upwards from80% of the combined weights of methylene chloride and methanol 'withabout 90% or more preferred. These solutions generally contain smallamounts of water, from about 0.3% of the weight of the solution up tothe amount which will create turbidity, although preferably water ispresent in no more than 60% by weight of the amount which will createturbidity. The amount of water which will create turbidity will varywith the composition of the solution. With the minimum concentration of15% by weight of cellulose triacetate in the solution and about ofmethanolin the solvent the turbidity point will correspond to about 1.7%of water.

Following spinning, the amount of stabilizer adhered to the cellulosetriacetate is extremely small and any small residual amounts will beremoved during the wet treatments to which fabrics made from saidfilamentary materials are normally subjected.

The following examples are given to illustrate the invention further.

EXAMPLE I Cellulose acetate having an acetyl value of 59.5% is dissolvedin a mixture of 91 parts by weight of methylene chloride and 9 parts byweight of methanol to form a solution having a concentration ofcellulose acetate of 21.5% by weight based on the weight of the solvent.On spinning this solution at the rate of 100 meters per minute at atemperature of 85 C. through chromium plated stainless steel jets 1 inchin diameter having holes each 0.036 mm. in diameter it is found that thejets corrode and one or more holes thereof become clogged within lessthan 100 hours. The presence of iron can be detected in the yarn.

EXAMPLE II To compare quantitatively the corrosive action of dopes ofdifferent composition, strips of hot rolled mild steel measuring inch by/s inch by 2% inches are immersed in the dopes for 14 days at 50 C.without agitation and the extent of corrosion of the strips isdetermined. The dopes in this comparison all are initially 15% by weightsolutions of cellulose acetate (61.5% acetyl value) in a 91/9 weightmixture of methylene chloride/methanol. Where water or inhibitor isindicated, the percentage is based on the total weight of the dope. Theresults are shown in the following table:

The dopes containing the Z-hydroxypropylamine nitrite and the cadmium2-ethyl hexoate are suitable for spinning and solvent recovery withlittle or no corrosion of metal equipment contacted therewith.

It is to be understood that the foregoing detailed description is merelygiven by way of illustration and that many variations may be madetherein without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patentis:

1. A stable composition of matter, non-corrosive on metals contactedtherewith, comprising a solution in a 4 halogen-containing organicsolvent of a lower alkanoic acid ester of cellulose and a stabilizingproportion of a member selected from the group consisting of a hydroxylower alkyl amine nitrite and a cadmium salt of a waterinsoluble fattyacid.

2. A composition ofmatter according to claim 1, wherein said solventcontains up to about 20% by weight of a lower alkanol,

3. A stable composition of matter, non-corrosive on iron contactedtherewith, comprising a solution in a chlorine-containing organicsolvent of a lower alkanoic ester of cellulose, said solution containingat least about 0.005% by weight of a hydroxy lower alkyl amine nitriteas a stabilizer.

4. A stable composition ,of matter, non-corrosive on iron contactedtherewith, comprising a solution of cellulose triacetate in methylenechloride, said solution containing about 0.005 to 0.5% by weight of ahydroxy lower alkyl amine nitrite as a stabilizer.

5. A stable composition of matter, non-corrosive on iron contactedtherewith, comprising a solution of cellulose triacetate in aconcentration of at least 15% by weight in a solvent comprisingmethylene chloride and a lower alkanol, the methylenechlorideconstituting at least about by weight of thesolvent, saidsolution containing about 0.005 to 0.5 by weight of Z-hydroxypropylaminenitrite as a stabilizer.

6. A stable composition of matter, non-corrosive on iron contactedtherewith, comprising a solution of cellulose triacetate in aconcentration ranging from about 17 to 27% by weight in a solventcomprising about by weight of methylene chloride and about 10% by weightof methanol, said solution containing water in an amount between aminimum of about 0.3% by weight and a maximum of the amount which willbring the solution to the turbidity point, said solution furthercontaining about 0.005 to 0.5% by weight of 2-hydroxypropylamine nitriteas a stabilizer.

7. A stable composition of matter, non-corrosive on metals contactedtherewith, comprising a solution of cellulose triacetate inmethylene-chloride, said solution containing a stabilizing proportion of2-hydroxypropy1 amine nitrite.

8. The process for stabilizing a solution against corrosion of metalcontacted therewith, said solution comprising a lower alkanoic acidester of cellulose dissolved in a halogen-containing organic solvent,which process comprises incorporating a stabilizing proportion of ahydroxy lower alkyl amine nitrite in said solution.

9. The process for stabilizing a solution against corrosion of metalcontacted therewith, said solution comprising cellulose triacetatedissolved in methylene chloride, which process comprises incorporating astabilizing proportion of Z-hydroxypropylamine nitrite in said solution.

10. In the production of filamentary material wherein a solution of alower alkanoic acid ester of cellulose in a halogen-containing organicsolvent is extruded through an orifice in a metallic member underconditions such that said cellulose ester is converted tofilamentarymaterial, the improvement which comprises incorporating in said solutiona stabilizing proportion of a hydroxy lower alkyl amine nitrite, wherebycorrosion of said metallic member and transfer of metal to said solutionand said filamentary material are inhibited.

11. In the production of filamentary material wherein a solution ofcellulose triacetate in methylene chloride is extruded through anorifice in a metallic member under conditions such that said cellulosetriacetate is converted to filamentary material, the improvement whichcomprises incorporating a stabilizing proportion of 2-hydroxypropylaminenitrite in said solution, whereby corrosion of said metallic member andtransfer of metal to said solution and said filamentary material areinhibited.

12. A stable composition of matter, non-corrosive on iron contactedtherewith, comprising a solution in a chlorine-containing organicsolvent of a lower alkanoic ester of cellulose, said solution containingat least about 0.005% by weight of a cadmium salt of a water-insolublefatty acid as a stabilizer.

13. A stable composition of matter, non-corrosive on iron contactedtherewith, comprising a solution of cellulose triacetate in methylenechloride, said solution containing about 0.005 to 0.5% by weight of acadmium salt of a water-insoluble alkanoic acid as a stabilizer.

14. A stable composition of matter, non-corrosive on iron contactedtherewith, comprising a solution of cellulose triacetate in aconcentration of at least 15% by weight in a solvent comprisingmethylene chloride and a lower alkanol, the methylene chlorideconstituting at least about 80% by weight of the solvent, said solutioncontaining about 0.005 to 0.5% by weight of cadmium 2-ethyl hexoate as astabilizer.

15. A stable composition of matter, non-corrosive on iron contactedtherewith, comprising a solution of cellulose triacetate in aconcentration ranging from about 17 to 27% by weight in a solventcomprising about 90% by weight of methylene chloride and about by weightof methanol, said solution containing water in an amount between aminimum of about 0.3% by Weight and a maximum of the amount which willbring the solution to the turbidity point, said solution furthercontaining about 0.005 to 0.5% by weight of cadmium 2-ethyl hexoate as astabilizer.

16. A stable composition of matter, non-corrosive on metals contactedtherewith, comprising a solution of cellulose triacetate in methylenechloride, said solution containing a stabilizing proportion of cadmium2-ethy1 hexoate.

17. The process for stabilizing a solution against corrosion of metalcontacted therewith, said solution com proportion of cadmium Z-ethylhexoate in said solution.

19. In the production of filamentary material where in a solution of alower alkanoic acid ester of cellulose in a halogen-containing organicsolvent is extruded through an orifice in a metallic member underconditions such that said cellulose ester is converted to filamentarymaterial, the improvement which comprises incorporating in said solutiona stabilizing proportion of a cadmium salt of a water-insoluble fattyacid, whereby corrosion of said metallic member and transfer of metal tosaid solution and said filamentary material are in-' hibited. V s

20; In the production of filamentary material wherein a solution ofcellulose triacetate'in methylene chloride is extruded through anorifice in a metallic member under conditions such that said cellulosetriacetate is converted to filamentary material, the improvement whichcomprises incorporating a stabilizing proportion of cadmium 2-ethylhexoate in said solution, whereby cor-' rosion of said metallic memberand transfer of metal to said solution and said filamentary material areinhibited.

References Cited in the file of this patent I UNITED STATES PATENTS2,278,747 Swezeyet al'. Apr. 7, 1942 2,419,327 Wachter et a1. Apr.22,1947 2,499,551 White Mar. 7, .1950 2,596,450

Wachter et a1. May 13, 19 52

1. A STABLE COMPOSITION OF MATTER, NON-CORROSIVE ON METALS CONTACTEDTHEREWITH, COMPRISING A SOLUTION IN A HALOGEN-CONTAINING ORGANIC SOLVENTOF A LOWER ALKANOIC ACID ESTER OF CELLULOSE AND A STABILIZING PROPORTIONOF A MEMBER SELECTED FROM THE GROUP CONSISTING OF A HYDROXY LOWER ALKYLAMINE NITRITE AND A CADMIUM SALT OF A WATERINSOLUBLE FATTY ACID.